High-conversion reduction synthesis of porous silicon for advanced lithium battery anodes

Abstract

For practical implementation of high-capacity silicon anodes, porous silicon (pSi) structures have demonstrated outstanding cycling stability against the large volume changes typical of solid silicon particles. The conventional magnesiothermic reduction (MR) of silica under static conditions limits the yield of pSi and sometimes produces low-purity of pSi owing to limited mass transfer and many side reactions. Hence, we devise a rotational MR (R-MR) system with rapid magnesium transport in which a uniform Mg/SiO2 molar ratio is readily achievable, and a short reaction time can be applied. Compared to conventional MR, the R-MR process has an extremely high yield (∼90 wt%) of pSi at almost complete conversion of precursor, whereas side reactions are substantially suppressed. Mg 2p X-ray photoelectron spectroscopy analysis of the reduction product reveals that pSi yield is well correlated with the conversion of Mg to MgO. The carbon-coated pSi/C samples and their hybrids with graphite (pSi/C@Gr) composites demonstrate stable cycling performance for 300−600 cycles at high capacity with high cycling efficiency (∼99.9%). Therefore, high-conversion R-MR can be a very efficient and scalable process for obtaining pSi for use in carbon composites (such as pSi/C and pSi/C@Gr) that offer outstanding cycling performance in high-capacity anodes for high-energy LIBs.